Chromium nitride layer for magnetic recording medium

ABSTRACT

A magnetic recording media with a multilayer structure and methods for forming the media are described. The magnetic recording media includes a substrate, an underlayer on top of the substrate and a magnetic layer over the underlayer. The underlayer includes a CrN film formed by sputter depositing chromium in the presence of nitrogen or nitrogen containing compounds.

BACKGROUND OF THE INVENTION

This invention relates to magnetic recording media and in particular tothe layered structure of the magnetic recording media.

There are many different forms of mass data storage technology used inmodern computing. One of the prevailing forms of data recording ismagnetic data recording due to its large capacity and re-usablerecording media. Magnetic data recording may be implemented utilizingdifferent types of magnetic recording media, including tapes, harddisks, floppy disks, etc. There is an ever increasing need for magneticrecording media with higher storage capacity, lower noise, and lowercosts.

The structure of a typical thin film magnetic recording disk ismultilayered and includes a substrate at its base covered by one or morelayers of thin film followed by a magnetic layer and optionally anotherlayer on top of the magnetic layer. The magnetic layer may be coatedwith an overcoat and/or an organic lubricant. The magnetic layer is themain body on which the magnetic bits are recorded.

Magnetic recording media can be longitudinal magnetic recording mediaor, more recently, perpendicular magnetic recording media. Perpendicularrecording media have many advantages over longitudinal recording mediaand are currently the more preferred magnetic recording media.

The composition of a magnetic layer can vary but can include suchcompounds as FePt or CoPt as described, for example, in US Patent Appln,Publication US2004/0191578 to Chen et al. The quality of the magneticlayer is in part determined by the layer or layers between the substrateand the magnetic layer. Important magnetic properties, for example,coercivity which are crucial to the recording performance of a disk candepend primarily on the microstructure of the various thin film layers.

A seedlayer disposed between a substrate and an underlayer is describedin Lee et al. in U.S. Pat. No. 5,800,931. The seedlayer described in Leeet al. is a MgO sputter deposited thin film. An underlayer havingchromium, a chromium alloy or a material having a B2 ordered crystallinestructure is then placed on the seedlayer prior to forming the magneticlayer. Formation of a seedlayer using MgO can lead to slow process timesin production. High quality crystals of MgO, which are crucial for anoptimal magnetic recording medium, are difficult to obtain and can alsolengthen the processing time in production.

SUMMARY OF THE INVENTION

A magnetic recording medium comprising a substrate, an underlayercomprising a CrN film and a magnetic layer.

A method for producing a magnetic recording medium comprises sputteringchromium in the presence of nitrogen or a nitrogen containing compoundonto a substrate to form an underlayer comprising a CrN film and forminga magnetic layer over the underlayer.

Another aspect of the invention includes a heat assisted magneticrecording medium comprising a substrate, an underlayer that is a thermalresistor comprising a CrN film and a L1₀ magnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a magnetic recording medium.

FIG. 2 is a schematic side view of a magnetic recording medium with aseedlayer below the underlayer.

FIG. 3 is a schematic side view of a magnetic recording medium with aseedlayer above the underlayer.

FIG. 4 is a schematic side view of a magnetic recording medium with anunderlayer between two seedlayers.

FIG. 5 a is a diagram of a B1 phase crystallographic lattice structure.

FIG. 5 b is a diagram of a L1₀ phase crystallographic lattice structure.

FIG. 6 is a XRD scan of a CrN film at different Psi tilt angles.

FIG. 7 is a XRD scan of FePt film grown on a CrN film.

FIG. 8 is a XRD rocking curve of CrN(200) peak.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The magnetic recording media described herein have a multilayerstructure and generally include a substrate, an underlayer formed on thesubstrate and a magnetic layer. By underlayer is meant a layer betweenthe magnetic layer and the substrate. The underlayer includes chromiumsputtered onto a substrate. Preferably the chromium sputtering isconducted in the presence of nitrogen or nitrogen containing compoundssuch that a film of CrN is formed over the substrate. The CrN film mayalso be sputter deposited from a CrN target with or without the presenceof nitrogen. A magnetic layer may be deposited directly on the CrNunderlayer.

In alternative embodiments, a seedlayer may also be included in themagnetic recording medium. A seedlayer, as referred to herein, is a thinlayer and can be formed between the substrate and the underlayer and/orbetween the underlayer and the magnetic layer.

One embodiment, illustrated by FIG. 1, includes magnetic recordingmedium 100. The recording medium 100 includes substrate 102 upon whichan underlayer 108 is formed. The underlayer 108 is formed by sputteringchromium in the presence of nitrogen or nitrogen containing compounds. Amagnetic layer 120 is formed over underlayer 108. An overcoat layer 124is deposited over magnetic layer 120.

FIG. 2 illustrates a schematic side view of an alternative embodiment ofmagnetic recording medium 100. Magnetic recording medium 100 includesseedlayer 106-a disposed between substrate 102 and underlayer 108.Magnetic layer 120 is formed over underlayer 108 and an overcoat layer124 is deposited over magnetic layer 120.

FIG. 3 illustrates another alternative embodiment of magnetic recordingmedium 100 with substrate 102. Seedlayer 106-b is formed over underlayer108. Magnetic layer 120 is placed over seedlayer 106-b followed byovercoat layer 124.

FIG. 4 illustrates a schematic side view of another alternativeembodiment of magnetic recording medium 100 with substrate 102.Seedlayer 106-a is formed over substrate 102. Underlayer 108 isdeposited by sputtering chromium in the presence of nitrogen or nitrogencontaining compounds over seedlayer 106-a. Seedlayer 106-b is formedover underlayer 108 followed by addition of magnetic layer 120 overseedlayer 106-b. Overcoat layer 124 is placed over magnetic layer 120.Seedlayer 106-a and seedlayer 106-b may be the same film, for exampleMgO. Alternatively, the seedlayers can be made from differentcomponents.

A variety of substrates can be used in the magnetic 5 recording mediadescribe herein. The substrate is generally formed of a nonmagneticmaterial. Suitable materials for the substrate can include, for example,high temperature glass, Si, ceramic glass, amorphous glass, NiP platedAlMg, sapphire, quartz, canasite, and SiC. Other suitable materials forsubstrates are known to those skilled in the art and are all within thescope of the description herein.

The underlayers of the magnetic recording media described herein arefabricated by reactively sputtering chromium in the presence of nitrogenor nitrogen containing compounds to form a CrN film. Sputtering is usedin the formation of thin films in construction of magnetic recordingmedia and is a well known technique in the art. Preferably, the chromiumsputtering is performed in a N₂ atmosphere. The CrN film may also befabricated by reactively sputtering chromium in a NH₃ atmosphere. TheCrN film may be sputter deposited in other Nitrogen containingatmospheres. The CrN film may also be sputter deposited from a CrNtarget with or without the presence of nitrogen.

The crystal structure and the texture of the underlayer are generallyimportant parameters for the optimal functioning of the magneticrecording media. A variety of crystal structures and textures of theunderlayer may be amenable in the magnetic recording media describedherein. The crystal structure of the CrN film of the underlayer is,preferably, a B1 phase structure. FIG. 5 a is a schematic diagram of acrystallographic cubic lattice structure in a B1 phase with a latticeparameter of “a”. The sputtered CrN film described herein, preferably,has a B1 crystal structure. The lattice parameter of the CrN film is,preferably, close to the lattice parameter of the magnetic layer used inthe recording media. When the lattice parameters of the underlayer andthe magnetic layer are closely matched, a better texture transfer canoccur between the underlayer and the magnetic layer. In one exemplaryembodiment, the lattice parameter of the CrN film is about 0.414 nm.Values of the CrN film lattice parameter, preferably, do not vary bymore than about 5% from this value. Values for the lattice parameteroutside of this range are also within the scope of this invention.

The underlayer formed by chromium sputtering, preferably, attains aperpendicular (200) texture during the growth of the CrN thin film. Thistexture is preferable for a magnetic layer with an L1₀ phase crystalstructure. The CrN film, preferably has a distribution angle of lessthan about 6°. More preferably, the CrN film has a distribution angle ofabout 4.5°. The thickness of the CrN film in the recording mediadescribed herein can be between about 1 nm and about 50 nm. Preferably,the thickness of the CrN film is between about 10 nm and about 20 nm.

The CrN film underlayer shows thermal resistance. Thermal resistance canbe measured, for example, by DELCOM 717 conductance Monitor obtainedfrom Delcom Instruments, Inc. Prescott, Wis. The CrN film underlayer canact as an insulator. In heat assisted magnetic recording (HAMR), thermalresistor layer is an important component of the medium structure. TheCrN film can be used as the thermal resistor of HAMR media, Preferably,the CrN film acts as an insulator and the conductivity measured by theabove mentioned instrument is zero.

The magnetic layer of the recording media can include a variety ofcomponents. The magnetic recording media may be longitudinal orperpendicular. In preferred embodiments, the magnetic recording media isperpendicular. The magnetic layer described herein, preferably containsa L1₀ phase crystal structure. FIG. 5 b is a schematic diagram of acrystallographic lattice structure in L1₀ phase with lattice parametersof “a” and “c”. Magnetic layers with a L1⁰ phase crystal structure thuscontain lattice parameters “a” and “c”. Suitable magnetic layers caninclude, for example, FePt, CoPt and FePd. A FePt magnetic layer, forexample, has a lattice parameter “a” of about 0.385 nm and parameter “c”of about 0.371 nm. Similarly, CoPt has a lattice parameter “a” of about0.380 nm and parameter “c” of about 0.370 nm and FePd has a latticeparameter “a” of about 0.385 nm and “c” of about 0.372 nm. Values of thelattice parameter for the L1₀ phase magnetic layer, preferably, do notvary by more than about 5% from these values. Vales for the latticeparameter outside of these range are also within the scope of thisinvention.

An overcoat layer may be provided over the magnetic layer as shown inFIG. 1-4. The overcoat layer provides a mechanical wear layer and can bebetween about 2.5 nm and about 30 nm. The overcoat layer is generally aninert layer and does not affect the function of the magnetic recordingmedia. The overcoat layer is preferably carbon based.

The recording media described herein may optionally include a seedlayer.The presence of the seedlayer is not necessary but in some embodimentsmay enhance the functioning of the recording media. As shown in FIG. 2,a seedlayer may be formed between the substrate and the underlayer. Theseedlayer can be any thin film that is compatible S with the CrN textureand crystal structure. Preferably, the seedlayer is a MgO layer that issputter deposited onto the substrate. The seedlayer preferably has a(200) texture similar to the CrN film. The seedlayer generally has athickness of less than about 5 nm.

In other embodiments, as shown, for example, in FIG. 3, a seedlayer maybe formed between the underlayer and the magnetic layer. In alternativeembodiments, as shown, for example, in FIG. 4, the magnetic recordingmedium can include two seedlayers. As described above, one seedlayer canbe disposed between the substrate and the underlayer and the secondseedlayer is placed between the underlayer and the magnetic layer. Boththe seedlayers can be the same. Alternatively, the seedlayers can bedifferent. In preferred embodiments, the seedlayers are MgO thin filmlayers.

A method for producing magnetic recording media is also contemplated inthis description. The method for producing magnetic recording mediaincludes sputter depositing chromium in the presence of nitrogen ornitrogen containing compounds onto a substrate to form a CrN filmunderlayer. The method further includes forming a magnetic layer,preferably a L1₀ phase magnetic layer, over the CrN underlayer. Anovercoat layer may be formed over the magnetic layer.

In some embodiments, the method may include forming a seedlayer betweenthe substrate and the CrN film. The seedlayer is preferably formed bysputter depositing MgO onto the substrate prior to forming theunderlayer. In other embodiments, the method may include forming aseedlayer between the CrN film and the magnetic layer. The seedlayer ispreferably formed by sputter depositing a MgO layer on top of the CrNfilm prior to forming the magnetic layer.

In other alternative embodiments, the method may include forming twoseedlayers. The seedlayer can be formed between the substrate and theunderlayer and between the underlayer and the magnetic layer. Both ofthe seedlayers may be sputter deposited MgO films. Alternatively, one ofthe seedlayers can be another compatible thin film.

EXAMPLE

A high temperature glass and Si substrate was used to produce a magneticrecording medium. A CrN film was fabricated onto the substrate byreactively sputtering Cr in a N₂ atmosphere. The sputtering wasconducted in a Cirulus M-12 sputtering chamber manufactured by Oerlikon,Liechtenstein. A sputtering production assembly line includes a seriesof chambers through which the substrate passes unidirectionally withcontrolled parameters. Sputtering was performed at room temperature at apressure of about 5 mTorr with pure nitrogen gas. A FePt L1₀ phasemagnetic layer was grown over the CrN film. An overcoat was placed overthe magnetic layer.

FIG. 6 shows an X-ray Diffraction (XRD) scan at different Psi tiltangles. The scan shows that reactive sputtering of Cr in N₂ forms a CrNfilm (not Cr or Cr₂N). The CrN film has a B1 phase crystal structure. Asshown in the XRD scan of FIG. 7, the FePt film grown on top of the CrNfilm has inherited the perpendicular texture. The XRD rocking curve ofFIG. 8 shows that the CrN film has a texture distribution angle of about4.5°.

It is to be understood that even though numerous characteristics andadvantages of various aspects have been set forth in the foregoingdescription, together with details of the structure and function ofvarious aspects, this is illustrative only, and changes may be made indetail, especially in matters of structure and arrangement of parts tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A magnetic recording medium comprising: a substrate; an underlayercomprising a CrN film having a B1 phase crystal structure; a firstseedlayer comprising MgO disposed between the substrate and the CrNunderlayer; and a magnetic layer.
 2. The recording medium of claim 1wherein the CrN film is formed by sputter depositing chromium in thepresence of nitrogen or nitrogen containing compounds.
 3. The recordingmedium of claim 1 wherein the CrN film has a (200) texture.
 4. Therecording medium of claim 1 wherein the thickness of the underlayer isless than about 50 nm.
 5. The recording medium of claim 1 wherein theCrN layer has a texture distribution angle of less than about 5°.
 6. Therecording medium of claim 1 wherein the magnetic layer is a L1₀ phasemagnetic layer.
 7. The recording medium of claim 1 wherein the magneticlayer has a (001) texture.
 8. The recording medium of claim 1 whereinthe magnetic layer comprises FePt.
 9. The recording medium of claim 1wherein the magnetic layer comprises CoPt.
 10. The recording medium ofclaim 1 wherein the substrate is glass, silicon, or an aluminum alloycoated with NiP.
 11. The recording medium of claim 1 further comprisinga second seedlayer between the CrN underlayer and the magnetic layer.12. The recording medium of claim 1 wherein the thickness of theseedlayer is less than about 5 nm.
 13. A heat assisted magneticrecording medium comprising: a substrate; a thermal resistor underlayercomprising a CrN film having a B1 phase crystal structure; a firstseedlayer comprising MgO disposed between the substrate and theunderlayer; and a L1₀ magnetic layer.
 14. The heat assisted magneticrecording medium of claim 13 wherein the CrN film is formed by sputterdepositing chromium onto the substrate in the presence of nitrogen andnitrogen containing compounds.